The present invention relates to a grid for a battery plate which is produced by a rotary expander, a method of producing it, and a battery using it.
A battery plate of a lead storage battery is configured by filling an active material into meshes of a grid made of lead or a lead alloy. Such a grid is often produced by directly forming a grid-like shape by means of, for example, casting of lead or a lead alloy, or alternatively by forming meshes in a metal sheet made of lead or a lead alloy (hereinafter, a sheet such as that containing lead, a lead alloy, or another alloy is referred to merely as a metal sheet) by an expander. The expander is of the reciprocal type in which meshes are sequentially formed in a metal sheet with starting from both the ends of the sheet, by vertical motions of a die cutter, or of the rotary type in which slits are formed in a zigzag pattern by rotation of a disk cutter, and the metal sheet is stretched from both the sides to develop the slits into meshes. As shown in FIG. 37, in a disk cutter 1 which is used in the rotary expander, large numbers of ridges 1a and valleys 1b are alternately formed at regular intervals along a circumferential direction on the peripheral side face of a metal disk. The valleys 1b are curved faces consisting of the circumferential face itself constituting the peripheral side face of the disk of the disk cutter 1. The oval enlarged view in FIG. 37 shows the circumferential face in a form developed to a plane. Each of the ridges 1a is formed by protruding the circumferential face of the disk cutter 1 in a ridge-like shape toward the outer periphery. The apex of the ridge is rounded and formed with being shifted toward the front side in the rotational direction (indicated by the arrow in the figure).
In the disk cutter 1, grooves 1c are formed in both the disk-like faces and in every other valley 1b. Each of the grooves 1c is a groove which has a width that is equal to the length (the distance between adjacent ridges 1a) of the corresponding valley 1b, and a depth that is about one half of the thickness of the valley 1b (the thickness of the disk cutter 1), and which is radially formed in the disk face of the disk cutter 1. The groove 1c is formed so as to open in the valley 1b in the outer peripheral side and have a length of some degree toward the center. The grooves 1c which are formed in every other valley 1b are arranged so as to be alternate on both the faces.
A large number of such disk cutters 1 are arranged on a common rotation shaft with being separated from each other by a distance which is approximately equal to the thickness of the disk cutters 1, thereby forming a disk cutter roll. As shown in FIG. 38, two disk cutter rolls each configured by a large number of such disk cutters 1 are vertically arranged, and a lead sheet 2 is passed between the rolls, thereby forming slits 2a. In this case, as shown in FIG. 39(a), the upper and lower disk cutter rolls are placed respectively at levels which allow the valleys 1b of the upper and lower disk cutter 1 to slightly overlap with each other. Furthermore, the upper and lower disk cutter rolls are placed with being shifted in the axial direction by a half pitch so that each of the disk cutters 1 of the lower disk cutter roll is positioned between the disk cutters 1 of the upper disk cutter roll. The rotational phase is adjusted so that, when the valley 1b in which the groove 1c is formed in one disk face of the upper disk cutter 1 reaches the lower end, the valley 1b in which the groove 1c is formed in the other disk face of the lower disk cutter 1 reaches the upper end, and, when the ridge 1a of the upper disk cutter 1 reaches the lower end, as shown in FIG. 39(b), the ridge 1a of the lower disk cutter 1 reaches the upper end.
When a metal sheet 2 is passed between the disk cutter rolls, as shown in FIG. 38, the slits 2a are formed in the metal sheet 2 by the ridges 1a of the upper and lower disk cutters 1, and thin wires 2b between the slits 2a which are formed adjacently in the width direction of the metal sheet 2 are pressed by the upper and lower ridges 1a to alternately vertically protrude in a ridge-like shape. As shown in FIG. 39(a), in the valleys 1b of the upper and lower disk cutters 1 where the grooves 1c face each other in opposite directions, the metal sheet 2 is cut so that the slits 2a are continuously formed, and, in the valleys where the grooves 1c face each other, the metal sheet 2 is not cut so that the slits 2a are intermitted to form nodes 2c. In the metal sheet 2, therefore, the slits 2a each having a length corresponding to two ride-like shapes which are formed by pressing of the ridges 1a are continuously formed in the transportation direction while being intermitted in the nodes 2c. Adjacent ones of the slits 2a are similarly continuously formed while their nodes 2c are shifted from each other by a half pitch. Therefore, the slits 2a are formed in a zigzag pattern as shown in a plan view which is in a circle of FIG. 38.
The metal sheet (lead sheet) 2 in which the many slits 2a are formed as described above is stretched toward both the sides in the width direction in a subsequent step. As a result, as shown in FIG. 40, the slits 2a are widened so as to form meshes, whereby a lattice-like grid is formed in which the nodes 2c are connected to one another by four wires 2b that are obliquely bent to be drawn out.
As shown in FIG. 47, endmost disk cutters 4 are disposed on both the axial ends of the lower disk cutter roll, respectively. In each of the endmost disk cutters 4, as shown in FIGS. 48 and 49, ridges 4a and valleys 4b are alternately arranged in the peripheral edge. The valleys 4b, and grooves 4c which are formed in the valleys 4b are configured in the strictly identical manner as the valleys 1b and the grooves 1c of the usual disk cutters 1. In each of the ridges 4a, however, a peripheral side face configured by a reference circumferential face is formed. Namely, in the endmost disk cutters 4, the ridges 4a do not protrude in a ridge-like shape toward the outer periphery, and the valleys 4b do not have a shape which is relatively recessed with respect to the ridges 4a. The endmost disk cutters 4 are placed at the ends of the lower disk cutter roll so as to be outward juxtaposed with the usual disk cutters 1 at the ends of the upper disk cutter roll, respectively.
In the ends of the disk cutter rolls, as shown in FIG. 47(b), the ridges 4a of the endmost disk cutters 4 of the lower disk cutter roll overlap with the ridges 1a of the end disk cutters 1 of the upper disk cutter roll, whereby the metal sheet 2 between the ridges are cut so that the slits 2a are formed and the wires 2b downward protrude in a ride-like shape. As shown in FIGS. 47(a) and 47(c), also in the adjacent portions (the right end in FIG. 47(a), and the left end in FIG. 47(b)) where the grooves 4c of the valleys 4b of the lower endmost disk cutters 4, and the grooves 1c of the valleys 1b of the upper end disk cutters 1 face each other in opposite directions, the valleys 1b and 4b slightly overlap with each other, whereby the metal sheet 2 is cut and the slits 2a are continuously formed. However, in the adjacent portions (the left end in FIG. 47(a), and the right end in FIG. 47(b)) where the grooves 4c of the valleys 4b of the lower endmost disk cutters 4, and the grooves 1c of the valleys 1b of the upper end disk cutters 1 are formed in the opposed faces so as to face each other, the grooves 1c and 4c cause the peripheral side faces of the valleys 1b and 4b not to overlap with each other, and the metal sheet 2 is not cut. Therefore, endmost nodes 2f which are similar to the nodes 2c are formed. Since no slit 2a is formed in the outer end, the endmost nodes 2f are directly connected to frame portions 2g which are formed in the ends in the width direction of the metal sheet 2.
The metal sheet 2 in which the many slits 2a are formed as described above is stretched toward both the sides in the width direction in the subsequent step of the rotary expander. As a result, as shown in FIG. 50, the slits 2a are widened so as to form meshes, whereby a lattice-like grid is formed in which the nodes 2c and the endmost nodes 2f are connected to one another by four wires 2b that are obliquely drawn out. In practice, the nodes 2c are pulled by the wires 2b during the developing step to be inclined in a twisting direction. In FIG. 50, however, such twist is omitted and the grid is diagrammatically shown.